U.S. patent number 6,834,179 [Application Number 10/060,529] was granted by the patent office on 2004-12-21 for method for operating an access control system, in particular for a motor vehicle, and access control system.
This patent grant is currently assigned to Siemens Aktiengesellschaft. Invention is credited to Nikolas Bergerhoff.
United States Patent |
6,834,179 |
Bergerhoff |
December 21, 2004 |
Method for operating an access control system, in particular for a
motor vehicle, and access control system
Abstract
In the access control system, a code transmitter-end transceiver
unit and a vehicle-end transceiver unit emit signals approximately
synchronously on approximately the same carrier frequency. As a
result of superimposition, a new code signal arises and its code
information item is compared with an expected set point code
information item. When there is correspondence, an enable signal
for locking or unlocking or releasing the immobilizer is generated.
The synchronous transmission/reception makes illegitimate
monitoring more difficult.
Inventors: |
Bergerhoff; Nikolas
(Regensburg, DE) |
Assignee: |
Siemens Aktiengesellschaft
(Munich, DE)
|
Family
ID: |
8176342 |
Appl.
No.: |
10/060,529 |
Filed: |
January 30, 2002 |
Foreign Application Priority Data
|
|
|
|
|
Jan 30, 2001 [EP] |
|
|
01102067 |
|
Current U.S.
Class: |
455/59; 340/5.63;
340/7.25; 375/267; 455/101; 455/102; 455/137; 455/273; 455/60;
455/61 |
Current CPC
Class: |
B60R
25/04 (20130101); B60R 25/24 (20130101); G07C
9/00309 (20130101); G07C 2009/00793 (20130101); G07C
2009/00388 (20130101); G07C 2009/00555 (20130101) |
Current International
Class: |
B60R
25/04 (20060101); G07C 9/00 (20060101); G08B
005/22 (); H04B 007/00 (); H04B 001/00 (); H04B
001/06 (); H04B 007/02 () |
Field of
Search: |
;340/5.7,5.71,5.72,5.61-5.64,10.1,10.41 ;455/59-61,101-102,137,500
;375/267 ;380/31 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Horabik; Michael
Assistant Examiner: Hamilton; Kimberly
Attorney, Agent or Firm: Greenberg; Laurence A. Stemer;
Werner H. Mayback; Gregory L.
Claims
I claim:
1. A method of operating an access control system, the access
control system including: a first transceiver unit in a portable
code transmitter configured to emit a first signal upon being
triggered; and a second transceiver unit in an access-controlled
system configured to emit a second signal upon being triggered; the
method which comprises the following steps: emitting the first
signal with the first transceiver unit and, at least partially
simultaneously and at a substantially equal carrier frequency,
emitting the second signal with the second transceiver unit,
whereby a superposition of the first signal and the second signal
forms a code signal; extracting a code information item from the
code signal; and comparing the extracted code information item with
a set point code information item, and generating an enable signal
if correspondence is determined between the code information item
and the set point code information item.
2. The method according to claim 1, wherein the access control
system is a motor vehicle access control system and the second
transceiver unit is disposed in the motor vehicle.
3. The method according to claim 1, wherein the extracting step
comprises extracting the code signal in the portable code
transmitter and in the access-controlled system, the comparing step
comprises comparing the code information item in the portable code
transmitter and in the access-controlled system with a respective
set point code information item, and the generating step comprises
generating the enable signal only if correspondence is determined
in the portable code transmitter and in the access-controlled
system.
4. The method according to claim 1, which comprises emitting a
start signal with the first transceiver unit or with the second
transceiver unit, and starting a transmission of the first signal
and of the second signal a fixed time period after receiving the
start signal.
5. The method according to claim 1, which comprises triggering a
challenge/response dialog between the portable code transmitter and
the access-controlled system upon receiving the enable signal.
6. The method according to claim 2, which comprises forwarding the
enable signal to a security assembly in the motor vehicle,
whereupon the security assembly is released when authorization is
proven.
7. The method according to claim 1, wherein, in order to generate
the first signal and the second signal, a respectively
corresponding code secret is stored in the access-controlled system
and the in portable code transmitter.
8. The method according to claim 1, which comprises generating the
first signal and the second signal by newly calculating the first
and second signals with a computational algorithm in such a way
that at every transmission the code signal contains a new code
information item.
9. The method according to claim 1, which comprises generating the
first signal and the second signal by newly calculating the first
and second signals with a computational algorithm in such a way
that at every transmission the code secret is transmitted in
encrypted form at a start of each transmission.
10. The method according to claim 1, which comprises emitting the
signals at a carrier frequency selected from the group of
frequencies consisting of approximately 315 MHz, approximately 433
MHz, and approximately 868 MHz.
11. The method according to claim 1, which comprises emitting with
the portable code transmitter a start information item at the start
of the first signal, whereby the second transceiver unit is
synchronized to the portable code transmitter.
12. The method according to claim 6, which comprises, after the
challenge/response dialog is successfully terminated, generating a
further enable signal with which the security assembly is
enabled.
13. The method according to claim 1, wherein the second transceiver
unit and the first transceiver unit are configured to transmit and
receive signals synchronously.
14. An access control system, comprising: a first transceiver unit
in a portable code transmitter configured to emit a first signal
upon being triggered; and a second transceiver unit in an
access-controlled system configured to emit a second signal upon
being triggered; wherein said first transceiver unit and said
second transceiver unit emitting the first signal and the second
signal at least temporarily overlapping and at a substantially
equal carrier frequency, whereby a superposition of the first
signal and the second signal forms a code signal; whereby the code
signal arising from the superimposition of the first signal and of
the second signal is received by said first transceiver unit and by
said second transceiver unit, and said first and second transceiver
units are configured to extract a code information item from the
code signal; and a comparator in at least one of said portable
transmitter and said access-controlled system for comparing the
respectively extracted code information item with a set point code
information item, and wherein an enable signal is generated if
correspondence is found between the code information item and the
set point code information item.
15. The access control system according to claim 14, wherein said
access-controlled system is a motor vehicle.
Description
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for operating an access control
system, with which the access, in particular to a motor vehicle, is
enabled only when authorization is proven by means of a code
transmitter.
In a prior art anti-theft system (see U.S. Pat. No. 5,552,641 and
German patent DE 43 29 697 C2), the user of the vehicle carries on
his person what is referred to as an electronic code transmitter
(for example in the form of a chip card) for unlocking his vehicle.
As soon as an activation means on the motor vehicle, for example a
door handle, is actuated, the vehicle-end control unit brings about
the emission of a request signal. If the request signal is received
in the code transmitter, the latter automatically transmits back
its response code signal which is characteristic of it, in order to
prove with the signal its authorization to use the motor vehicle.
If the response code signal is recognized as being authorized, the
doors of the motor vehicle are unlocked.
A challenge/response dialog, that is an enquiry with a challenge
signal and a response with a response signal, takes place in an
analogous fashion if the user is in the interior of the vehicle and
wishes to start the vehicle. Given authorization of the code
transmitter, the immobilizer is then released and the motor vehicle
can be started.
Potential car thieves can monitor the signals which are transmitted
in wireless fashion between the vehicle and the code transmitter
and illegitimately reproduce them in order to obtain access to the
motor vehicle.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method of
operating an access control system and a corresponding access
control system, especially for motor vehicles, which overcome the
above-mentioned disadvantages of the heretofore-known devices and
methods of this general type and wherein monitoring and
reproduction of the transmitted signals is made more difficult. In
particular, the intention is to check in the motor vehicle whether
the received response signal originates from a legitimate code
transmitter which is assigned to the motor vehicle, or whether the
signal has in fact been reproduced by an unauthorized person.
With the foregoing and other objects in view there is provided, in
accordance with the invention, a method of operating an access
control system, in particular an access control system of a motor
vehicle. The access control system includes a first transceiver
unit in a portable code transmitter configured to emit a first
signal upon being triggered; and a second transceiver unit in an
access-controlled system (e.g., a motor vehicle) configured to emit
a second signal upon being triggered;
The method comprises the following steps: emitting the first signal
with the first transceiver unit and, at least partially
simultaneously and at a substantially equal carrier frequency,
emitting the second signal with the second transceiver unit,
whereby a superposition of the first signal and the second signal
forms a code signal; extracting a code information item from the
code signal; and comparing the extracted code information item with
a set point code information item, and generating an enable signal
if correspondence is determined between the code information item
and the set point code information item.
In other words, the objects are achieved by a method for operating
an access control system in which a dialog takes place between the
motor vehicle and the code transmitter on the same carrier
frequency. At the same time, both a vehicle-end transceiver unit
and an electronic code transmitter transmit within predefined time
periods (overlapping of transmission phases). As a result, the
emitted signals overlap in these time periods. The overlapping
signal which arises in this way is the new characteristic code
signal whose coded contents are evaluated and checked for
authorization.
For a potential thief there is the problem that at one location
(within the transmission and reception range of the transceiver
unit of the vehicle or in the transmission and reception range of
the code transmitter) he must, on the one hand, reproduce a
monitored signal and at the same time monitor a signal on the same
carrier frequency. This is largely prevented with the method
according to the invention because the synchronous transmission of
the monitored signal interferes with the receiver used for the
monitoring (same carrier frequency).
In accordance with an added feature of the invention, the
extracting step comprises extracting the code signal in the
portable code transmitter and in the access-controlled system, the
comparing step comprises comparing the code information item in the
portable code transmitter and in the access-controlled system with
a respective set point code information item, and the generating
step comprises generating the enable signal only if correspondence
is determined in the portable code transmitter and in the
access-controlled system.
In accordance with an additional feature of the invention, a start
signal is emitted with the first transceiver unit or with the
second transceiver unit, and a transmission of the first signal and
of the second signal is started a fixed time period after receiving
the start signal.
In accordance with another feature of the invention, a
challenge/response dialog is triggered between the portable code
transmitter and the access-controlled system upon receiving the
enable signal, and/or the enable signal is forwarded to a security
assembly in the motor vehicle, whereupon the security assembly is
released when authorization is proven.
In accordance with a further feature of the invention, in order to
generate the first signal and the second signal, a respectively
corresponding code secret is stored in the access-controlled system
and the in portable code transmitter.
Preferably, the first signal and the second signal are generated by
newly calculating the first and second signals with a computational
algorithm in such a way that at every transmission the code signal
contains a new code information item.
It is also possible for the first signal and the second signal to
be generated by newly calculating the first and second signals with
a computational algorithm in such a way that at every transmission
the code secret is transmitted in encrypted form at a start of each
transmission.
In a preferred embodiment of the invention, the signals are emitted
at conventional carrier frequencies of approximately 315 MHz,
approximately 433 MHz, or approximately 868 MHz.
In accordance with again an added feature of the invention, a start
information item is emitted with the portable code transmitter a
start at the start of the first signal, whereby the second
transceiver unit is synchronized to the portable code
transmitter.
In accordance with again an additional feature of the invention,
after the challenge/response dialog is successfully terminated, a
further enable signal is generated with which the security assembly
is enabled.
Finally, it is possible for the second transceiver unit and the
first transceiver unit to transmit and receive signals
synchronously.
With the above and other objects in view there is also provided, in
accordance with the invention, an access control system,
comprising: a first transceiver unit in a portable code transmitter
configured to emit a first signal upon being triggered; and a
second transceiver unit in an access-controlled system configured
to emit a second signal upon being triggered; wherein the first
transceiver unit and the second transceiver unit emitting the first
signal and the second signal at least temporarily overlapping and
at a substantially equal carrier frequency, whereby a superposition
of the first signal and the second signal forms a code signal;
whereby the code signal arising from the superimposition of the
first signal and of the second signal is received by the first
transceiver unit and by the second transceiver unit, and the first
and second transceiver units are configured to extract a code
information item from the code signal; and a comparator in at least
one of the portable transmitter and the access-controlled system
for comparing the respectively extracted code information item with
a set point code information item, and wherein an enable signal is
generated if correspondence is found between the code information
item and the set point code information item.
In accordance with a concomitant feature of the invention, the
access-controlled system is a motor vehicle.
Other features which are considered as characteristic for the
invention are set forth in the appended claims.
Although the invention is illustrated and described herein as
embodied in a method for operating an access control system, in
particular for a motor vehicle, and access control system, it is
nevertheless not intended to be limited to the details shown, since
various modifications and structural changes may be made therein
without departing from the spirit of the invention and within the
scope and range of equivalents of the claims.
The construction and method of operation of the invention, however,
together with additional objects and advantages thereof will be
best understood from the following description of specific
embodiments when read in connection with the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a motor vehicle with an anti-theft system according to
the invention, and
FIGS. 2, 3 and 4A to 4D show pulse diagrams of signals which are
transmitted between the vehicle and the code transmitter in the
anti-theft system according to FIG. 1.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring now to the figures of the drawing in detail and first,
particularly, to FIG. 1 thereof, an anti-theft system for a motor
vehicle has a vehicle-end transceiver unit 1 which can emit and
receive signals via one or more antennas 2. The transceiver unit 1
is controlled by a control unit 3 for transmitting or receiving and
for modulating or demodulating signals. The evaluation of the
received and demodulated signals preferably takes place in the
control unit 3.
In addition, the anti-theft system has a portable code transmitter
4 (referred to in FIG. 1 as an ID tag) which also has a transceiver
unit. The code transmitter-end transceiver unit can transmit and
receive signals via one or more non-illustrated antennas. In
particular, it transmits a code information item which is
characteristic of the code transmitter 4 and with which the code
transmitter 4 proves its authorization to lock or unlock the motor
vehicle or to release the immobilizer.
The lock system and the immobilizer are security assemblies which
can be controlled by means of the code transmitter 4 given
authorization.
With reference to FIG. 2, if a user manually actuates a triggering
means (door handle or switch on or in the vicinity of the door
handle) on the motor vehicle, a wake-up signal 9 is firstly emitted
by the vehicle-end transceiver unit 1. If a code transmitter 4
receives the wake-up signal 9, it firstly transmits a start signal
5, which has the purpose of bringing about chronological
synchronization between the transceiver unit of the code
transmitter 4 and the transceiver unit 1 of the vehicle.
Directly after the emission or even after a fixed time period
.tau.+.delta..sub.1 after the emission of the start signal 5, the
code transmitter 4 transmits a first signal 7. Directly after the
reception or even after a fixed time period .tau. after the
reception of the start signal 5, the vehicle transmits a second
signal 6 in a chronologically overlapping fashion (overlapping the
time period .delta..sub.3) with the first signal 7.
The start signal 5 can, of course, also be emitted by the
transceiver unit 1 in the motor vehicle in order to synchronize the
code transmitter 4 and the vehicle-end transceiver unit 1.
The essential feature for the invention is that the first signal 7
and the second signal 6 are emitted approximately synchronously on
the same carrier frequency, so that the two signals 6 and 7 overlap
partially or chronologically in certain periods (by the time period
.delta..sub.3 in the exemplary embodiment). As a result of the fact
that the two signals are transmitted approximately synchronously, a
superimposition signal (referred to below as code signal CS) which
is received both by the code transmitter-end transceiver unit and
by the vehicle-end transceiver unit 1 arises.
The code signal CS contains a code information item which is
composed of the code information items of the first and of the
second signal 6, 7, and can be evaluated both by the transceiver
unit 1 and by the code transmitter 4.
For this purpose, the code information item is compared with a set
point code information item. Only if there is correspondence with
the set point code information item is an enable signal generated,
as a result of which either the security assemblies are enabled or
an challenge/response dialog between the motor vehicle and the code
transmitter 4 is triggered, which dialog can then lead to the
security assembly being enabled if there is authorization. In the
challenge/response dialog there is no longer any need for
chronological overlapping of the signals 6 and 7.
The first signal 7 and the second signal 6 are emitted on
approximately the same carrier frequency in a chronologically
overlapping fashion and are advantageously amplitude-modulated (AM
modulation). One possibility for the AM modulation is the OOK
(On-Off Keying), wherein the carrier signal is switched on and off
in the clock of the modulation. Instead of switching off the
carrier signal completely, it can also be transmitted with greatly
reduced amplitude.
Binary signals are transmitted with a specific electrical signal
shape. All known methods are possible for this, for example the NRZ
method or the Manchester coding method (cf. FIG. 3). The Manchester
coding method is advantageously used in motor vehicle engineering
because it is particularly suitable for clock recovery, and thus
for bringing about synchronization between the transmitter and
receiver.
In FIG. 3, part of a binary code information item with the logic
values "0" and "1" of the individual bit is illustrated. This code
information item can be represented by NRZ signals (Non Return to
Zero) with the logic states "H" and "L" for each bit. Such a signal
can be represented, for example, in the Manchester code (coded
format). In the Manchester code, a carrier oscillation (which
oscillates with the carrier frequency) within a bit (i.e. within
the pulse period T of a single bit) is keyed once completely (or
even only partially, that is to say with reduced amplitude) and is
not keyed at all once with respect to the amplitude (also referred
to as on-off keying). A signal with the logic value "1" is
generated by a pulse of the length T/2 in the first half of the
pulse period T, while a signal with the value "0" is generated by a
pulse train with the length T/2 in the second half. The envelope
curve which is actually obtained (ideally it would be a square-wave
oscillation) is illustrated by a dotted line in a sinusoidal shape
in FIG. 3.
The signals 6 and 7 are structured in such a way that in specific
time periods .delta..sub.1, only the vehicle-end transceiver unit 1
transmits, in specific time periods .delta..sub.2 only the code
transmitter-end transceiver unit transmits, and in specific time
periods .delta..sub.3 both the vehicle and the code transmitter
emit a carrier oscillation synchronously (cf. FIG. 2). The code
signal CS comprises the entire time period .delta..sub.1
+.delta..sub.2 +.delta..sub.3.
The individual pulse trains of the respective signals 6, 7 do not
need to have uniform signal periods. They can have a different
signal period at each emission. The signal periods can be
generated, for example, by random generators in the transceiver
unit 1 and/or code transmitter 4. To make correct detection of the
transmitted code information items possible, the respective signal
period of the respectively received unit is fed into in encrypted
form.
Carrier frequencies of 315 MHz, 433 MHz or 868 MHz are
advantageously used because they are already used today for radio
remote control in motor vehicle equipment and have also received
approval in a large number of countries. Of course, other carrier
frequencies can also be used. However, it is a precondition that
both the vehicle-end transceiver unit 1 and the code
transmitter-end transceiver unit operate with the same carrier
frequency.
The generation of the code signal CS from the first signal 7 and
from the second signal 6 will be explained in more detail below by
way of example with reference to FIGS. 4A to 4D. Here, the start
signal 5 and the first signal 7 of the code transmitter 4 are
illustrated in FIG. 4A in the form wherein they are transmitted by
said code transmitter 4.
FIG. 4B illustrates a signal such as is received by the code
transmitter 4. FIG. 4C illustrates the second signal 6 which is
emitted by the transceiver unit 1, and FIG. 4D illustrates a signal
such as is received by the transceiver unit 1 in the motor
vehicle.
The signal illustrated in FIG. 4A is advantageously a valid
Manchester-coded signal (indicated by the numerals "1" and "0").
The letter "a" marks, in FIGS. 4A to 4D, time periods wherein no
carrier signal can be transmitted or received. The letter "b" marks
time periods wherein a carrier signal is transmitted or received.
In FIGS. 4B and 4D, the height of the signal periods illustrated
indicates the reception field strength (amplitude). This is always
particularly high if the local transmitter transmits a carrier
signal because the receiver receives more strongly a carrier signal
which is emitted in the direct vicinity than a carrier signal which
is transmitted from a remote transmitter.
In addition, FIGS. 4B and 4D also show decision thresholds S.sub.1
and S.sub.2. Below the respective decision threshold S.sub.1 or
S.sub.2, the respective receiver decides on "no carrier signal"
(corresponds to the state "a"), and above the decision threshold
the respective receiver decides on "carrier signal present"
(corresponds to the state "b").
In the invention, the second signal 6 is emitted via the
transmitting antenna 2 of the vehicle-end transceiver unit 1, and
the first signal 7 is emitted via the transmitting antenna (not
illustrated) of the code transmitter 4. On the one hand the signal
transmitted by its own transmitting antenna and the signal
transmitted by the opposite end are received by means of the
respective receiving antennas.
However, one end receives only the signal emitted by itself as long
as its amplitude is greater than zero (i.e. this end is in this
case "deaf" for the other end) and one end then only receives the
signal of the other end and if it does not transmit itself (i.e.
the transmission amplitude is zero). For this reason, the code
transmitter 4 and the vehicle-end transceiver unit 1 are tuned to
one another with respect to the emitted code information item. This
can be fed into the parts when the parts are programmed at the end
of the line at the vehicle manufacturer or can be newly calculated
by a computational algorithm before each transmission
(computational algorithm is implemented in an initialization or
programming operation).
The code transmitter 4 firstly starts with a number of start bits
(start signal 5; cf. FIG. 4A), as a result of which the code
transmitter 4 and the vehicle-end transceiver unit 1 are
synchronized. Both the vehicle-end transceiver unit 1 and the code
transmitter 4 can emit a start signal 5, the transmission of the
first signal 7 and of the second signal 6 as a result of the
received start signal 5 being started at a fixed time period after
that.
In the exemplary embodiment, the code transmitter 4 transmits a
number of start bits and then the code information item
"abababbabaababab" (FIG. 4A). Before or after the code information
item it is also possible to transmit further control information
items which must not influence the code information item.
The vehicle-end transceiver unit 1 transmits its code information
item approximately synchronously with the code information item of
the code transmitter 4, specifically "abbaaabbbaaabbaa" in the
present exemplary embodiment (FIG. 4C). According to FIG. 4B, the
code transmitter 4 receives both the code information item emitted
by it itself (this is largely unattenuated, i.e. with somewhat
large amplitude) and the code information item of the vehicle-end
transceiver unit 1 (this is somewhat attenuated, i.e. with somewhat
smaller amplitude, because the code transmitter 4 and the
transceiver unit 1 are at a distance from one another).
However, the code transmitter 4 does not "monitor" those amplitudes
of the oscillation states of the code information item emitted by
the vehicle-end transceiver unit 1 at those times at which the
oscillation states are those of its own transmitted code
information item "b".
The code transmitter 4 has a threshold value switch with a
threshold value S.sub.1. According to the received amplitudes, the
code transmitter 4 evaluates the signal by comparison with the
threshold value S.sub.1. All the amplitudes which are greater than
the threshold value S.sub.1 are evaluated as oscillation state "b",
while all the amplitudes which are smaller than the threshold value
S.sub.1 are evaluated as oscillation state "a". The code
transmitter 4 thus evaluates the code information item CS:
"abbbabbbbaabbbab" from the received superimposition signal.
According to FIG. 4D, the vehicle-end transceiver unit 1 receives
both the code information item emitted by it itself (this is
largely unattenuated, i.e. with somewhat larger amplitude) and the
code information item of the code transmitter 4 (this is somewhat
attenuated, i.e. with somewhat smaller amplitude because the code
transmitter 4 and the transceiver unit 1 are at a distance from one
another).
The vehicle-end transceiver unit 1 also has a threshold value
switch with a threshold value S.sub.2. The vehicle-end transceiver
unit 1 evaluates the received signal in accordance with the
received amplitudes. All the amplitudes which are greater than the
threshold value S.sub.2 are evaluated as oscillation state "b",
while all the amplitudes which are smaller than the threshold value
S.sub.2 are evaluated with the oscillation state "a". In this way,
the transceiver unit 1 obtains the code information item CS:
"abbbabbbbaabbbab" from the received superimposition signal, which
code information item is correctly identical to that of the code
transmitter 4.
An unauthorized person in the region of the code transmitter 4 who
monitors the code signal received there can only reproduce said
code signal with errors so that no authorization can then be
proved.
The reliability of the method can be additionally increased by
differentiating not only between the states "a" and "b" but also by
additionally evaluating the absolute amplitude level of the
received signal.
The set point code information can be stored as a corresponding
code secret either in the vehicle-end transceiver unit 1 or in the
control unit 3. Only if the received code information item of the
code signal CS corresponds to the set point code information is an
enable signal for enabling a security assembly generated.
The set point code information item can also be stored as a
corresponding code secret in the code transmitter 4. Only if the
code information item received by it is identical to the set point
code information item is the code transmitter 4 enabled further
functions and further transmission of signals (for example further
challenge/response dialog which can only then lead to the enabling
of the security assembly).
The code information item is advantageously compared with the set
point code information item both in the code transmitter 4 and at
the vehicle end in the transceiver unit 1 or in the control unit 3.
Only in this way is it possible to force a potential thief to have
to transmit and monitor in both directions synchronously, in order
to be able to simulate a correct code signal CS. However, as
previously described, synchronous transmission and monitoring can
be achieved only with extreme difficulty owing to the same carrier
frequency, so that effective protection against manipulation is
provided.
The set point code information item and the code information item
can also be generated from a code secret stored in the code
transmitter 4 or in the vehicle-end transceiver unit 1/control unit
3, using a mathematical algorithm or some other logic connection.
The code secret is fed to the parts during an initialization
operation and permanently stored in a way which is protected
against reading out from the outside.
The vehicle-end transceiver unit 1 and the control unit 3 can be
accommodated in a common housing. The vehicle-end transceiver unit
1 can have a single transmitting and receiving antenna 2, provided
that this antenna 2 can transmit and receive synchronously.
Transmitting and receiving antennas which are separated from one
another can also be arranged in the motor vehicle. A plurality of
transmitting antennas and a plurality of receiving antennas can
also be arranged in the motor vehicle and also on the code
transmitter 4.
The antennas 2 are arranged distributed in the motor vehicle and
are configured in such a way that, as far as possible, all the
regions in the motor vehicle or in the direct vicinity of the motor
vehicle are penetrated with an electromagnetic field using one
transmission signal (this corresponds to the range of the signals).
Conversely, signals are then reliably received from these
regions.
The term code transmitter 4 is to be understood--irrespective of
its external form--as a device which receives a signal and
transmits back a coded signal. The code transmitter 4 can be
arranged here on a chip card/check card, in a keygrip or other
housings. The code transmitter 4 can be used as a security assembly
for remotely controlling a locking system of a motor vehicle and an
immobilizer without using a mechanical key. The code transmitter 4
usually has a transponder which automatically transmits back a
signal as a result of a received signal.
The transponder usually obtains its voltage supply for the
transmission of a signal from the electromagnetic field of the
received signal. The transponder can also be supplied with power
via its own battery or via a storage battery.
The challenge/response dialog is to be understood as being a
bidirectional communication between the transceiver unit and the
code transmitter 4, during which communication a first, received
enquiry signal serves as a trigger for the emission of a response
signal. A plurality of challenge/response dialogs can also take
place, in order to prove authorization for releasing the
immobilizer or for locking and unlocking the locking system.
The first signal 7, the second signal 6 and the enable signal (as
well as the enquiry signal and the response signal of the
challenge/response dialog) are coded signals which each have a code
information item. The code information item is a binary coded
information item which has a large number of bit places. As a
result of the coding/encrypting, the code information item changes
at each new encryption process. The code information item can be
preceded or followed by a plurality of bits which may be required
for a reliable transmission of data. The code information item
which is extracted from a received signal is compared with a stored
or generated set point code information item.
The first signal 7 and the second signal 6 can also be divided into
a plurality of sections and each emitted in sections, the
respective sections also being transmitted with at least partial
chronological superimposition.
The method for operating an access control system is not restricted
to use only in a motor vehicle. It can also be used in other
objects such as buildings, security rooms, garages, personal
computers, mobile telephones, ATMs, chip cards or other devices
wherein there is an interrogation for authorization for access
control or for use.
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